Mg-Y-Zn合金三元金属间化合物的电子结构及其相稳定性的第一性原理研究

First-principles study of electronic structures and phase stabilities of ternary intermetallic compounds in the Mg-Y-Zn alloys

采用基于密度泛函的第一性原理平面波赝势方法计算Mg-Y-Zn合金三元金属间化合物X-Mg_(12)YZn相和W-Mg_3Y_2Zn_3相的晶格常数、形成焓和电子结构.形成焓的计算结果表明,X-Mg_(12)YZn相和WMg_3Y_2Zn_3相都具有负的形成焓,并且W-Mg_3Y_2Zn_3相的形成焓更低;电子结构的计算分析表明,WMg_3Y_2Zn_3相成键峰主要来自Mg的2p轨道、Zn的3p轨道和Y的4d轨道的贡献.而X-Mg_(12)YZn相成键峰主要来自Mg的3s和2p轨道、Zn的3p轨道和Y的4d轨道的贡献.对W-Mg_3Y_2Zn_3相(011)面和XMg_(12)YZn相(0001)面的电荷密度分析表明,两相中Zn-Y原子间都形成了共价键,且W-Mg_3Y_2Zn_3相的共价性比X-Mg_(12)YZn相的共价性更强.在费米能级低能级处,W-Mg_3Y_2Zn_3相具有更多的成键电子数,决定了W-Mg_3Y_2Zn_3相比X-Mg_(12)YZn相有更好的相稳定性.

In the paper,the first-principles pseudopotential plane-wave method based on density functional theory is used to investigate the crystal structures,enthalpies of formation and electronic structures of X-Mg（12）YZn phase and WMg3Y2Zn3 phase in Mg-Y-Zn alloys.The obtained lattice constants of two phases are in good agreement with the available experimental values,which can reasonably reflect the accuracy of theoretical calculation.The calculated enthalpies of formation indicate that the W-Mg3Y2Zn3 and X-Mg（12）YZn phases have negative enthalpies of formation,which are-0.2787 eV/atom and-0.0268 eV/atom respectively.Both phases can form stable structures relative to single crystals Mg,Y and Zn,and the enthalpy of formation of W-Mg3Y2Zn3 phase is lower than that of X-Mg（12）YZn phase.The results for density of states show that the bonding of W-Mg3Y2Zn3 phase occurs mainly among the valence electrons of Mg 2p,Zn 3p and Y 4d orbits,the bonding peaks between-2.53 and 0 eV are derived from the hybridization of Mg2 p,Zn 3p and Y 4d orbits,the peaks between 5.07 and 7.51 eV predominantly originate from the hybridization of Mg 2p and Y 4d orbits.However,the bonding of X-Mg（12）YZn phase is mainly among the valence electrons of Mg 3s,Mg 2p,Zn3 p and Y 4d orbits.The bonding peaks between-2.30 and 0 eV originate mainly from 2p,3p,and 4d orbit hybridization of Mg,Zn and Y,the peaks between 0 and 2.08 eV originate from the hybridization of Mg 3s,Mg 2p,Zn 3p and Y 4d orbits.At the same time,there is a pseudo-gap near each Fermi level of W-Mg3Y2Zn3 and X-Mg（12）YZn phases,which implies the presence of covalent bonding in the two phases.In addition,the charge densities respectively on（011） plane of W-Mg3Y2Zn3 phase and（0001） plane of X-Mg（12）YZn phase are analyzed,and the results indicate that the Zn-Y band exhibits covalent features in W-Mg3Y2Zn3 phase and X-Mg（12）YZn phase,the covalent bonding of W-Mg3Y2Zn3 phase is stronger than that of X-Mg（12）YZn phase.Compared with X-Mg（12）YZn phase,W-Mg3Y2Zn3 phase has a good phase stability attributed to its more bonding electron numbers in a low-energy region of the Fermi level.